Heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating recording media to reduce the coercivity of the media so that the applied magnetic writing field can more easily direct the magnetization of the media during the temporary magnetic softening of the media caused by the heat source. For heat assisted magnetic recording (HAMR) a tightly confined, high power laser light spot is used to heat a portion of the recording media to substantially reduce the coercivity of the heated portion. Then the heated portion is subjected to a magnetic field that sets the direction of magnetization of the heated portion. In this manner the coercivity of the media at ambient temperature can be much higher than the coercivity during recording, thereby enabling stability of the recorded bits at much higher storage densities and with much smaller bit cells.
One approach for directing light onto recording media uses a planar solid immersion mirror (PSIM) or lens, fabricated on a planar waveguide and a near-field transducer (NFT), in the form of an isolated metallic nanostructure, placed near the PSIM focus. The near-field transducer is designed to reach a local surface plasmon (LSP) condition at a designated light wavelength. At LSP, a high field surrounding the near-field transducer appears, due to collective oscillation of electrons in the metal. Part of the field will tunnel into an adjacent media and get absorbed, raising the temperature of the media locally for recording.
HAMR is believed to be one of the candidates that will enable 1 Tb/in2 areal density or above. However, as the areal density increases, there are several issues for HAMR. One of the primary problems is how to control thermal spot size. The power absorption in the recording media is highly dependent on head to media spacing (HMS), power output from NFT or laser, etc. In such a system the typical power output depends inverse exponentially with HMS due to the evanescent decay of optical near field. Such variation will lead to variation of the thermal spot size. The down track variation will cause a small position jitter. Cross track variation will cause erasure and modulation of the track width, limiting the potential areal density achievable for HAMR.